Structural Regulation Of PBA Materials And Their Application In Lithium-sulfur Batteries

Lithium-sulfur batteries have become one of the most promising next-generation battery candidates due to their higher theoretical specific capacity and theoretical energy density(1675m Ah g^-1,2600 Wh kg^-1).However,because of the low conductivity of the cathode material sulfur and discharge products,the"shuttle effect"caused by the intermediate lithium polysulfide,lithium dendrites and other defects,the cycle performance and cycle life of the battery are limited.In order to solve the above problems,this paper reports the structural design of three-dimensional sulfur storage host and the modification strategy of separator based on Prussian blue analogue（PBA）as the precursor material,and deeply discusses its influence on the electrochemical performance.The main research content and results are as follows:（1）A composite sulfur electrode material（3-Mn Ni-PBA@S@PPy）coated with polypyrrole was prepared by one-step precipitation method and in situ coating method.Which was used to study its effect as a cathode on the electrochemical performance of lithium-sulfur batteries.It was found that a high initial capacity of 1285 m Ah g^-1 was released at a current density of 0.1 C,the decay rate is only 0.07%per cycle at a high current density of 0.5 C and a long cycle of 500 cycles.This is attributed to the recombination of nickel to regulate the microelectronic structure of the Mn-N6 bond and improve the structural stability of 3-Mn Ni-PBA@S@PPy.The coating of conductive polymer increases the conductivity of the material,the chemisorption of more abundant adsorption sites combined with the physical barrier of PPy can better adsorb polysulfides and selectively improve the kinetics of polysulfide conversion.（2）A layer-by-layer stacked heterostructure of MXene and Prussian blue analog PBA（MXene@PBA）was prepared using an end-group-directed self-assembly strategy,which was used as a sulfur host to study its effect on the electrochemistry of lithium-sulfur batteries.The results show that the MXene@PBA@S cathode material has an initial capacity of 1220 m Ah g^-1 at 0.1 C,it can still maintain 582.9 m Ah g^-1 after 500 cycles at 0.5 C,and the decay rate is only 0.31%per cycle.In the case of 3.0 mg cm^-2 high sulfur-loading and lean electrolyte,the areal specific capacity of 3.4 m Ah cm^-2 is released.This is due to the fact that the PBA synergistic MXene composite exhibits a strong polysulfide adsorption capacity and can bidirectionally accelerate the conversion of liquid-phase polysulfides to solid-phase polysulfides.（3）A cationic dual active site three-dimensional egg yolk structure oxide composite interface material（3DCS-FMO@C）was synthesized by soft template method,ion exchange method and pyrolysis method,modified commercial separator,and its influence on electrochemical performance was deeply explored.The results show an ultrahigh initial capacity of 1530 m Ah g^-1 at 0.1 C,and an ultra-low decay rate of 0.029%at 0.5 C for 1000cycles,even in the case of high sulfur addition(7.3 mg cm^-2)and poor electrolyte(6 u L mg^-1),a high areal specific capacity of 8.7 m Ah cm^-2was achieved at a current density of 0.1 m A cm^-2.The analysis shows that the double sites of Mn²⁺（octahedron）and Fe²⁺（octahedron）in 3DCS-FMO@C cooperate to adsorb polysulfides,which can effectively regulate the bidirectional conversion kinetics of intermediate liquid phase polysulfides and solid phase lithium sulfide,and lower the energy barrier for its reaction.Meanwhile,the lithium-philic properties in the3DCS-FMO@C modified separator with high mechanical stability and no reduction in ion diffusion enable it to homogenize the flow of lithium ions,thereby suppressing the growth of lithium dendrites.